With regard to a barrier bag having moisture-proof and light-shielding function, among packing materials for a light-sensitive material, there have been developed various techniques for ensuring physical strength, moisture-proof and light-shielding. For ensuring the strength, for example, materials described in Japanese Patent Open to Public Inspection Nos. 237640/1986, 181944/1987 and 283944/1988 (hereinafter referred to as Japanese Patent O.P.I. Publication) and Japanese Utility Model O.P.I. Publication No. 25538/1987 may be cited, and there have been known packing materials composed of substances described in Japanese Patent O.P.I. Publication Nos. 18547/1987, 289548/1988, 290741/1988, 270535/1989, 946341/1989 and 64537/1990 as a material wherein linear low density polyethylene (LLDPE) excellent in physical properties as a film is used.
For ensuring light-shielding property, there are used light-shielding substances such as those described in Japanese Patent O.P.I. Publication Nos. 85539/1988, 82935/1989, 209134/1989, 94341/1989, 165140/1990 and 221956/1990. For ensuring moisture-proof property, there are known packing materials wherein an aluminum foil or a evaporated foil is used such as those described in Japanese Patent O.P.I. Publication Nos. 77532/1989, 251031/1989, 186338/1990 and 278256/1990.
Conventional packing materials and manufacturing methods therefor will be explained concretely as follows.
As a simple method, there may be given a means in which a bottom of a carbon-black-containing black polyethylene tube made through an inflation method and having the thickness of 60-150 .mu.m is heat-sealed and cut to prepare a black polyethylene bag wherein light-sensitive materials are packed manually.
Bags having light-shielding property and strength described in Japanese Patent O.P.I. Publication Nos. 146539/1990 and 196238/1990 are also included in the embodiment mentioned above.
The inflation method, in this case, is a method in which a film tube extruded from a circular die attached on an extrusion machine is inflated with air gradually until it reaches its predetermined width, and then it is taken up after being flattened by nip rolls.
Incidentally, in the case of a tube made through an inflation method, it is necessary to make a tube having its own width. On the other hand, products of light-sensitive materials come in many kinds and sizes and a clearance between a packing bag and a product in the packing bag needs to be kept appropriate. Therefore, the number of sizes of packing bags has to be increased.
In general, therefore, it can not be avoided that the number of sides of bags is as many as 50 or more.
It is problematic from viewpoints of management and operation to prepare tubes in various sizes to cover all sizes of bags, and it adversely affected the producibility.
Further, what does matter most for the conventional bag is that the automatic packing is difficult.
As another embodiment, there is also used a bag made of a shut of a multi-layer structure wherein a heat-resistive material such as paper is laminated with a film having a light-shielding property and high mechanical strength as shown in FIG. 1a. As a light-shielding film having strength, in this case, there is generally used a sheet made of a carbon-black-containing black polyethylene tube made through the above-mentioned inflation method, the tube being cut at its both side edges before being taken up.
There is also known one wherein a laminate layer made of various materials is sandwiched between a heat resisting material and a light-shielding film. FIGS. 1a, 1b, 1c and 1d represent sectional views of various multi-layer structures for the sheet.
The heat resisting material or a heat resisting layer in this case is represented by paper as a typical one, and non-bleached, semi-bleached and bleached kraft papers are given as typical ones and their general weight is 45-190 g/m.sup.2 in which a range of 50-90 g/m.sup.2 is preferably used from the viewpoints of easy manufacturing of bags and strength thereof.
Further, heat-resisting material heat-resisting films such as polyethylene terephthalate, nylon or polypropylene may be used in addition to paper.
Laminated layers are formed by means of methods such as extrusion lamination, dry lamination, wet lamination and hot-melt lamination. When a web to be laminated is a resin film, methods of extrusion lamination and dry lamination are commonly used.
What does matter most for a packing material having heat resisting layers is that recycling is difficult after disposal because layers constituting a sheet, such as, for example, a heat resisting layer, a laminated layer, a moisture-proof layer, a film layer and a light-shielding strength layer are different in terms of materials and separation thereof is not easy.
When a metal such as aluminum or the like is used for a moisture-proof layer, there also is a problem that metallic residuary substances remain after incineration.
Further, examples in FIGS. 1a and 1b do not have any problem of physical strength, but examples in FIGS. 1c and 1d have problems of physical strength depending on a type of a heat resisting layer.
The inventors have found out that, in a conventional method for making a bag, when no heat resisting layer is provided, it is impossible to make a bag because an outer layer melts before an inner surface is sealed, or it is difficult to make a bag even it is possible to make because creases are caused and pinholes are frequently generated.